Coastal zones – seismic vulnerability an analysis from east coast of india

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 03 Special Issue: 16 | ICPECDM-2014 | Dec-2014, Available @ http://www.ijret.org 116
COASTAL ZONES – SEISMIC VULNERABILITY AN ANALYSIS FROM
EAST COAST OF INDIA
B. L. Narasayya1
1
Rtd. Dy. Director General G.S.I
Abstract
The paper briefly attempts at a conceptual approach on the reported events of moderate seismic activity from parts of East Coast
of India originating from the shallow depths of sea floor in a short span of less than two decades. As a passive continental margin,
it is assuring to feel a stable condition for the East Coast. But its Geotectonic critical position in the Bay with Andaman Islands
architecture on the east and further east the Indonesian Islands and experience of 2004 Tsunami of devastating nature hitting the
Southern East Coast necessitates that the geo technical frame has to be critically studied from the point of view of Active
Tectonics and as a mitigation measure appropriate building codes have to be implemented in seismic designs.
Keywords: seismic activity, geotectonic critical position, Tsunami, mitigation
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1. INTRODUCTION
Asia Pacific bears the brunt of many natural hazards. About
five million deaths took place in the 20th
century alone. The
human losses due to 26th
Dec. 2004 Tsunami are reported
over lakhs. One estimate is that about 60% of the area in
India is prone to earthquakes which frequent different high
risk zones like the Himalayan belt, the Eastern arc as well as
Continental interiors. The concept of the so called “Shield
area” has almost disappeared.
2. HAZARDS – A GEOPERSPECTIVE
The Geosphere comprising Lithosphere, Hydrosphere,
Atmosphere and Biosphere continuously undergoes
interactions among the different process variables resulting
in their manifestations such as earthquakes, volcanisms etc.
Cyclone, floods are entirely driven by atmospheric
hydrospheric regimes through the mechanism of solar
energy and forecasting is possible with the designated
process parameters. Earthquakes originate at the depths
either on land or on ocean beds, occasionally with
devastating Tsunamis affecting the contiguous landmasses.
There exists prediction component available for Tsunamis
on the data base and high-end technology. The Earth’s
evolution in time and space from the Achaean times to the
recent must have witnessed dramatic and Catastrophic
events such as episodes of volcanism, meteoric
bombardment with tectonic instability . The records of
deformation, earthquakes are often obliterated or sparsely
preserved in forms further to be decoded. The palaeo
earthquake records are dated through signatures in the
quaternary. Historical records (post human settlements and
civilizations) and logging gave us the some idea of the
occurrences of the earthquakes spread over different parts of
the globe even during the pre-instrumental days. With the
advent of a “Seismograph”, documented data had been
available notably from countries like China and later in
Japan in the year 79 A.D. with historical geological events
of volcanism at Pompeii and earthquakes in Italy, remained
a landmark for the strengthening of seismic and related
studies in critical affected areas . The available data over the
last two centuries only is spread over unevenly from
different parts of the world and often with diversity in
content of scientific parameters. But devastation in terms of
losses of lives and property is the biggest casualty to human
kind caused by earthquakes.
3. ANCIENT AND MIDIVIAL WORK
In India also ancient science has reached a very high
landmark even on the studies pertaining to earthquakes as
documented in the details of “Brihat Samihita” by
VARAHA MIHIRA as early as 6th
century A.D. giving
description to the areas likely to be affected and people in
those kingdoms along with the type of earthquakes as a
classification. Earthquakes were less a boon and more a
bane. Study of earthquakes provided us the knowledge of
earth’s interior. Credit goes to old hams work. The doors of
seismology were opened. Earlier renowned investigators
studied earthquakes and their effects. Prof. Celsius studied
in Gulf of Bothinia. Darwin studied on board HMS Beagle
in the areas of South America coast and Moho from
Balkans. An astronomer Schmidt studied earthquakes in
Rhine graben and in fact coined the term epiccentre. Earlier
phase of studies had a focus on surface affects,
modifications and even related rupture details to seismic
phenomena. The earliest catalogue of earthquakes and a
geological documentation originated in India. Even though
earthquakes were part of tectonic and thermal regimes right
from early crustal evolution, their documentation was only a
few centuries old after the advent of seismograph.

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 03 Special Issue: 16 | ICPECDM-2014 | Dec-2014, Available @ http://www.ijret.org 117
4. SOME SIGNIFICANT MODERN
CONTRIBUTIONS
The tectonic architecture of peninsular and extra peninsular
India has been worked out by many investigators ( Krishnan
(1982), Grady (1976), Mahadevan (1994), Mishra (2006),
Ravishanker (1995), Balakrishnan et.al., (2009) and
Valdiya(1976). In furtherance combining seismicity and
tectonics, emphasis has been laid on seismotectonics of the
entire regions. ( Chandra(1977), GSI (2000) documenting
the historic and cultural evidences, catalogues of
earthquakes had been prepared as early as nineteenth
century (Oldham 1883). With more and more data historical
seismicity has been given a thrust resulting in a workable
data base for further processing. Along with data from
organizations like GSI, IMD. Many contributors made
significant advances. (Rao and Rao 1984) In addition to
individual earthquakes being well studied and published.
Earthquakes in specific Geotectonic environments like
shield areas had received attention. (Gupta nd Gupta 2003).
Himalayan Seismogenesis and Plate Tectonic models of
Inida together with eastern and north-western neighbors has
remained as focus of global attention along with assessment
of seismic Hazard.. (Bilham et.al., 2001, Khattri et.al., 1984,
Ravikumar and Bhatia, 1999)
Thus, Seismic investigations have enabled newer insights
into the understanding of the earth’s internal layers and their
compositions, heterogeneity in the material media, presence
of liquid phases in the core etc. Earthquake studies began
from Geological Survey of India 1819 Rann of Kutch, 1892
Baluchistan earthquake, 1897 Assam earthquake and
recorded significant observations such as abrupt
modifications of ground surface. Oldham (1898) is one of
the earliest to recognize different Geological expressions,
ground ruptures etc. established that earthquakes are related
to faults. It may be emphasized that surface expressions of
earthquake faults can be more potentially utilized to have a
deeper insight the dynamics. However, there has been a shift
from the geological base of study more towards seismogram
analysis progressively and qualification in Hazard
assessment studies.
5. TECTONICS CONFIGURATION: AN
OUTLINE
The advent of Plate Tectonics has brought out many unified
facts regarding the distribution and trends of earthquake
zones globally. Plate boundaries are imaged by earthquake
epicenters. Briefly it may be stated that India’s tectonic
configuration comprise the following tectonomorphic
provinces .(Krishnan 1982, Balakrishnan 2009, Chandra
1977, Mahadevan 1994)
1. Himalayan belt and the Tertiary mobile belts on the
east and west.
2. Indo-Gangetic fore deep.
3. Peninsular shield (a mosaic of Archean nuclei with
peripheral proterozoic mobile belts.
4. Intra-continental basins.
5. Passive continental margins on east and west.
The Geotectonic set up of India is further characterised by
Andaman Nicobar Islands, 85 degrees – 90 degrees E ridges
on the east, Lakshadweep chagos, sea mounts and ridges on
the west.(Ravikumar and Bhatia 1999) . Further on the east,
countries like Indonesia, Malaysia, Japan have been
frequented by devastating earthquakes and Tsunamis.
India’s adjoining tectonic regimes on the east are far more
complex tectonically.
6. 2004 TSUNAMI
A devastating earthquake on the west coast of Sumatra
(Dec. 26th
2004) generated Tsunami hitting the Indian and
Sri Lankan coasts. Tsunami waves transgressed over a
lateral distance of 300-500m with a run-up elevation of a
maximum 5 meters in a few segments. The coast witnessed
emergence of new surfaces in the beach front, erosion of
spits, breaching along the coastline etc.
There had been reports of Tsunami and related hazards
following earthquakes in Indonesia and other island groups
on west of Indonesia. While Tsunamis are secondary effects
(though not in devastation) of earthquakes, as also
landslides, earthquakes are also secondary or consequent
upon volcanism at places like Western U.S. Yellow stone
area which are by and large non-tectonic in origin.
7. COASTAL ZONE – CONTINENTAL MARGIN
A coast is a geomorphic expression and which more or less
marks the outer landward limit of the oceans or seas or the
outer seaward limit of the land and is not a defined or
marked line. It oscillates between the highest high water tide
mark and lowest low water tide mark during the daily
cycles. Within a longer geological span, there are many
oscillations of sea level on a much wider zone, marks of
transgressions and regression cycles which are registered
through geological indicies. In the context of plate tectonics
with ocean basins and continents as two marked geomorphic
expressions, a continental margin marks the geological
boundary between the two domains. Further the continental
margins as tectonic domains, may be passive type (Atlantic)
or active type (Pacific). The passive margins and ocean
basins with, shelf, slope, rise etc. are considered to be
largely aseismic or stable. Maximum seismic energy is
released at the Pacific type active margins with subduction
related earthquakes of very high magnitudes. Active
margins are characterized by mountains, trenches and active
volcanoes with extreme topographic variations.
8. PENINSULAR INDIA & EAST COAST
The Geology of Peninsular India mainly comprises
Precambrian assemblages with Jurassic to Quaternary
sedimentary rocks and volcanics of Cretaceous-Eocene. The
on-shore and offshore regions of East coast are mainly
younger sequences with prospects of hydrocarbons. The
Coastal areas have undergone repeated cycles of sea level
changes during Quaternary. Prominent geomorphic elements
along the East Coast are Ganges, Brahmaputra delta,
Mahanadi, Godavari, Krishna, Penna and Cauvery deltas.

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 16 | ICPECDM-2014 | Dec-2014, Available @ http://www.ijret.org 118
(Fig.1) The Coastal risk along Peninsular Coast has been
worked out prior to the advent of cyclone of 2004 (Banerjee
et.at., 2001)
Later Inter-minittent seismic activity along parts of East
coast is reported around the following places from reports
during the period.
1 Off. Odisha coast, May, 2014.
2 Off. Visakhapatnam , Jan., 1996.
3 Off. Pondicherry, Dec., 2001.
The shallow depth origin and possible rejuvenation of faults
are broadly surmised in the above examples. Further general
observations along East Coast are as follows either on-
shore/off-shore. Evidences of uplift and subsidence are
reported. Further there are evidences of disturbances in the
top layers of sediments along parts of East Coast by way of
displacements in the layers as seen in the sub-bottom
profiles. There are also rise-like structures below the top
reflector. Presence of hot springs and field evidence
showing displacement on a small scale are noticeable on
ground. There are evidences of coarse sized sand and pebbly
rich aggregates of sediments on the deep sea floor at around
2500m depth beyond slope as observed at Off. Pennar. Such
exotic sediments are possibly seisomogenic turbidites (GSI
unpublished sea bed survey reports 1983-2000). Thus it is
prudent to infer seismic activity, neotectonism and upper
continental crust along East Coast at places.
9. EARTHQUAKES PROCESS VARIABLES:
By and large most of the earthquakes originate in the
lithosphere. The different levels of crustal layers have
geometrical disposition and possible seismogenic horizons.
There is compositional and mineralogical change from
upper crust towards more mafic-rich and then more
magesian rich. Pressures, temperatures and fluids affect the
degree of stability of the minerals and the rocks. The role of
pore fluids and fluid pressures in weakening the rock is
broadly well known but less experimentally documented.
Failure of materials , nucleation and nature of the
seismogenic crust are thus most valuable data base. The low
velocity zones are of value in critical sectors of seismic
source areas and seisomogenically vulnerable areas and in
revealing the nature of material through high resolution data
on density inferred through accurate velocities.
10. NEOTECTONICS -EARTHQUAKES
On a mega-scale the fragmentaed Indian Shield and recent
earthquakes are considered in conjunction as important.
(Ravishenkar 1995). Further uplift during neogene and
rejuvenation had been recognized as field evidences in the
younger geological column (Radhakrishna 1993)
A study of recent deformation of the crust geologically of
quaternary (and also Pleistocene and even Pliocene) forms
the main theme of neotectonics. Active tectonics are those
tectonic movements that are expected to occur within a
future time span of concern to society. Any fault that moved
in the last say 35,000 years (or 10,000 years) is considered
as active fault. Active Tectonics involves dynamic process
operating in the present day regimes. Sometimes there exists
a correlation between active faults and active volcanoes.
Combining active tectonics and records of reported
seismicity new generation maps or models of
seismotectonics could be framed combining the inputs of
Geology and Geophysics and Seismic Microzonation maps.
Existing seismic zonation maps have to be accelerated to
higher degree.
Pertaining to the East Coasts, for the last 200 years there are
no authentic historical records of seismicity of such reported
events or causalities. The extension of the continental crust
is well postulated together with active faults or those
rejuvenated along pre-existing faults. However, despite
moderate seismic activity reported along parts of East Coast
from the off shore there is no major seismic activity in the
area, so far, from these parts of passive margin. Prudently
such signs have to be read in holistic set up. The complex
tectonic elements on the East including the Burmese-arc,
Andaman archipelago, The Indonesian archipelago have
diverse spreading and converging elements and result in a
complicated dynamics. Seismic stability cannot be assumed
and preparedness is needed especially in view of 2004
Tsunami of Sumatra Earthquake.
-9-
11. FUTURE LOOK
Against the immense data available in respect of
earthquakes, their science an attempt towards progresses of
at least the vulnerability criteria could be a worthwhile
endeavor with the aid of all modern tools of geology,
geomorphology, geodesy, geo physics- geo chemistry and
remote sensing. As the only visible marking available is
though active faults and neotectonics for generating new
class of seismic hazardzonation maps, on priority of know
source zones and historical seismicity criteria, with
emphasis on the geodynamic factors. Though not the time
and place for forecasting the search for active faults through
available criteria and search for hidden faults through
geology centered techniques along with geophysics/ geo
chemistry analogies to search for hidden deposits should
become a programme of national endeavor for many reputed
national organizations and their teams. It is stressed that
strict implementation of building codes as per Bureau of
standards and appropriate seismic designs are adhered to in
future in all the vulnerable areas and as per zones indicated.
12. CONCLUSION
1. There has been a view that widely prevalent shield
area is largely considered to be stable. However, this
point of view has changed over as there are events of
both high magnitude seismicity dominantly in the
Himalayan belt and Eastern belt and moderate
events or difuse seismicity in the Central and
Southern parts of the country. The Coastal margins
on both East and West are specific with their
respective features.

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 03 Special Issue: 16 | ICPECDM-2014 | Dec-2014, Available @ http://www.ijret.org 119
2. The Eastern Coastal areas all along the peninsula
also witnessed moderate events of seismic nature as
evidenced by the recent reports from Off. Odisha
Coast, Off. Visakhapatnam and Off. Pondicherry
which are pointers towards Coastal domains as well
the adjoining margin areas. However, the tectono-
geomorphic set up changes form North to South.
3. In view of accelerated developmental programs and
even nuclear facilities likely along the east coast in
future mitigation measures such as earthquake
resistant designs need to be an integral part of design
and implementation.
4. Even large reservoirs need to be analyzed from
seismic vulnerability point of view as reservoir-
induced seismicity is also reported at places like
Koyana.
5. Microzonation needs to be taken in such sectors as
measures of Prognosis, Sub-surface geophysical
analysis and holistic surface geological criteria such
as active faults are visibly significant clues. These
can find place in new programmes to be pursued.
6. In view of mounting population, urbanization the
need for developmental facilities of high values,
prevalence of non-engineered structures as a rule,
even a minor or modulate nature in Coastal corridors
stands as a high risk factor at least a zone of around
50kms. Building codes, thus are a safe need with
designs of earthquakes and cyclone resistant
modules.
ACKNOWLEDGEMENTS
The author expresses his gratitude to GSI and the team
members of GSI who had been associated at various stages
in the data collection, processing and interpretation in
various projects on board the Research Vessels in Cruises.
The opinions expressed are general and those of the author
alone from efforts in synthesizing the unpublished data.
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